Views: 165 Author: Site Editor Publish Time: 2024-06-18 Origin: Site
| Wastewater Type | Painting wastewater treatment |
| Implementation time | 2019.10 |
| Processing scale | 540m3/D |
| Project name | Painting Process Wastewater Treatment Project for An Automobile Manufacturing Company in Zhejiang |
| Product name | Dissolved Air Flotation+Lamella Plate Clarifier+Sludge Dewatering |
| Process |
Table of contents（Click to go to where you want to see）
2.1 Wastewater treatment process introduction
2.2.1 Treatment of phosphating wastewater
2.2.2 Comprehensive wastewater pretreatment
2.2.3 Terminal wastewater treatment
2.2.4 Terminal wastewater advanced treatment
2.2.5 Sludge treatment system
2.2 Effects of wastewater treatment measures
2.3 Analysis of the treatment capacity of wastewater treatment facilities
Coating plays a vital role in the automobile manufacturing process. It can effectively prevent rust and corrosion and beautify the car's appearance.
However, coating production also brings more environmental problems. Among them, generating a large amount of wastewater brings trouble to enterprise governance, especially the cleaning and ultrafiltration wastewater generated by the electrophoresis process and the circulating water used to capture paint mist in the spray room. The pollutants are complex, high in concentration, and poor in biodegradability. If the appropriate treatment process cannot be selected, there will be more significant environmental risks.
This article introduces the electrophoretic coating wastewater treatment project of a new energy automobile manufacturing enterprise in Zhejiang. The project introduces how the enterprise chooses a wastewater treatment process suitable for the enterprise, considering the treatment efficiency and having a particular economy.
The coating process of a particular automobile manufacturing company is shown in Figure 1. The main methods include pre-cleaning, degreasing, cathode electrophoresis, UBS primer, weld thickness, satisfactory sealing, color paint spraying, varnish spraying, drying, inspection, inner cavity wax spraying, etc.
The wastewater generated in the coating production process of this company is shown in Table 1, mainly including flood flushing wastewater, degreasing wastewater, phosphating wastewater, electrophoresis wastewater, paint circulation wastewater, etc. The amount of sewage generated is shown in Table 2.
Figure 1 Coating process flow of an automobile manufacturing company
| Type of sewage | Production process | Main pollutants |
| Flood flushing wastewater | Wastewater generated by washing and cleaning processes during the painting process | Inorganic salts (alkali, phosphate, etc.), grease, heavy metals, etc. |
| Degreasing wastewater | Degreasing, wastewater generated in the process of removing grease from the car body by heating with a weak alkaline solution | SS, CODCr, BOD, petroleum, phosphate, etc. |
| Phosphating wastewater | The continuously discharged phosphating rinsing wastewater and regularly discharged phosphating tank liquid generated in the phosphating process | Phosphates, SS, metal ions, etc. |
| Electrophoresis wastewater | Post-electrodeposition rinse liquid and electrophoresis ultrafiltrate in the electrophoresis process | CODCr, SS, etc. |
| Grinding wastewater | Wastewater generated by wet grinding of car bodies | SS, solvents, additives, powders, etc. |
| Paint spraying wastewater | Circulating water used by the paint spraying room to capture paint mist during the painting process | CODCr, SS, etc. |
Table 1 Wastewater types and pollutants
| Pollution source | Daily wastewater volume/(m3·d-1) | Annual wastewater volume/(m3·a-1) | pH | Main pollutant generation concentration/(mg·L-1) | ||||||
| COD | Ammonia nitrogen | Petroleum | Phosphate | SS | Total zinc | Total nickel | ||||
| Flood flushing wastewater | 85.0 | 21250 | 9~11 | 5000 | 500 | 1500 | ||||
| Pre-degreasing, degreasing wastewater | 18.7 | 4675 | 11~13 | 9000 | 1000 | 1700 | 1000 | |||
| Degreasing wastewater | 181.5 | 45375 | 9~10 | 500 | 40 | 50 | 350 | |||
| Surface conditioning wastewater | 9.1 | 2275 | 9~10 | 280 | 500 | 100 | ||||
| Phosphating wastewater | 1.7 | 425 | 4~6 | 350 | 5000 | 250 | 400 | 200 | ||
| Phosphating wastewater | 206.5 | 51625 | 4~6 | 100 | 300 | 20 | 30 | 15 | ||
| Electrophoresis wastewater | 32.5 | 8125 | 2~6 | 1500 | 1000 | |||||
| Grinding wastewater | 0.5 | 125 | 6~9 | 3000 | 1000 | |||||
| Painting wastewater | 4.8 | 1200 | 8~9 | 5000 | 1500 | |||||
Table 2 The amount of painting wastewater of the automobile manufacturing enterprise
Given the water quality characteristics of painting wastewater, many automobile manufacturers currently use a combination of multiple technologies to carry out comprehensive treatment or treat a specific component separately. The combined treatment process involves various means, such as physical, chemical, and biological.
Among them, the most widely used combined process in automobile manufacturing is the physicochemical-biological method, which is also considered one of the wastewater combined treatment methods with development prospects.
The physicochemical-biological method first uses physical and chemical means to pre-treat suspended solids, heavy metals, etc., in the painting wastewater and then uses biological methods further to treat the biodegradable part of the pre-treated wastewater so that the treated wastewater can be recycled or discharged to meet the emission requirements.
The following is an analysis of the treatment process, treatment effect, and economic characteristics of the process through the wastewater treatment project case of the automobile manufacturer.
Wastewater treatment process introduction
This automobile manufacturing enterprise's total amount of painting wastewater is 540.3 m3/d. A phosphating wastewater treatment unit is set up to treat the phosphating wastewater separately and remove the heavy metal nickel in the wastewater.
For other wastewaters that do not contain nickel, pre-cleaning wastewater, degreasing and oil removal wastewater, phosphating tank liquid wastewater, electrophoresis electrodeposition flushing, ultrafiltration water, and paint mist capture circulating wastewater in the paint spraying room are first centrally pre-treated to remove most of the phosphates, oils, SS, and part of the COD, and then biochemically treated. Then, the wastewater is further terminally treated through multi-media filtration and ultrafiltration devices. The clean water produced after treatment is reused in production, and the concentrated water is combined with the treated phosphating wastewater to be discharged to the company's main drainage outlet, as shown in Figure 2.
Figure 2 Wastewater treatment process flow of the automobile manufacturing enterprise
The phosphating wastewater treatment process is "phosphating waste liquid dripping + coagulation and sedimentation." The phosphating waste liquid and wastewater containing the first-class pollutant nickel are treated by "phosphating waste liquid dripping + coagulation and sedimentation." The regularly discharged phosphating waste liquid is temporarily stored in the spare phosphating tank of the workshop and slowly added to the phosphating wastewater collection pool by dripping through the phosphating waste liquid collection tank of the pretreatment device and then combined with the phosphating wastewater for coagulation and sedimentation treatment.
Compared with the "secondary coagulation and sedimentation" process (phosphating waste liquid coagulation and sedimentation, and then combined with phosphating wastewater for coagulation and sedimentation), the "phosphating waste liquid dripping + coagulation and sedimentation" treatment process has stable effluent water quality (Ni content
0.1 ~ 0.2 mg / L), and a high total nickel removal rate of more than 99%.
The total nickel content in the treated phosphating waste liquid and wastewater reaches the "maximum allowable discharge concentration of the first-class pollutants" requirement of the comprehensive sewage discharge standard at the outlet of the treatment facility before being discharged to the outside.
Comprehensive wastewater pretreatment
Comprehensive wastewater mainly refers to the production of sewage without Ni generated by other processes in the coating workshop, and the pretreatment process is "coagulation + flotation sedimentation".
"rst, the other production wastewater without Ni is sent to the comprehensive wastewater regulating tank, pumped to the pH reaction tank to adjust the acidity and alkalinity of the wastewater, and then sent to the coagulation tank, and Ca(OH)2, CaCl2, PAC, PAM are automatically added to react to remove most of the phosphates, petroleum, SS, and part of COD, and demulsify at the same time. The mixed wastewater after the reaction is discharged into the dissolved air flotation sedimentation machine, and the flocs generated in the coagulation process are entirely precipitated and separated through solid-liquid separation; at the same time, the remaining floating oil in the wastewater is removed through flotation treatment, and the treated wastewater is discharged into the terminal wastewater treatment facility.
The terminal wastewater treatment process is SBR, responsible for treating water from other wastewater pretreatment facilities and domestic wastewater. The treated terminal wastewater is further treated in deep treatment facilities.
The SBR method is an activated sludge method developed in the 1980s. It is a wastewater biological treatment activated sludge process based on the degradation of organic matter, ammonia, nitrogen, and other pollutants in sewage by suspended microorganisms under aerobic conditions. It is a wastewater treatment technology widely recognized and adopted worldwide.
The terminal wastewater deep treatment process adopts "multi-media filtration + ultrafiltration + reverse osmosis." The clean water produced by the deep treatment device is reused in production, and the concentrated water is discharged to the company's main drainage outlet.
To ensure the effective operation of the ultrafiltration + reverse osmosis device (double membrane process), the system also sets a multi-media filtration device in the front section of the terminal wastewater deep treatment system to enhance the profound treatment operation effect.
During the wastewater treatment process, sludge will be generated, mainly physicochemical sludge generated by comprehensive wastewater pretreatment and biochemical sludge generated by terminal wastewater treatment.
Physicochemical sludge contains oil and heavy metals such as nickel and zinc and is a hazardous waste. The physicochemical sludge enters the sludge concentration tank and is initially concentrated to a less than 85% water content. It is then pumped into the chamber filter and pressed by the sludge pump for dehydration. The water content of the dehydrated sludge is about 60%. It is packaged and labeled according to the hazardous waste disposal method, temporarily stored in the company's hazardous waste room, and regularly handed over to qualified units for treatment; the biochemical sludge is dehydrated using the sludge tank and belt filter press equipped with the SBR device. The water content of the dehydrated sludge is about 60%, temporarily stored in the general solid waste storage room and regularly sent to the domestic waste treatment plant for disposal.
After sewage treatment stations treat the production wastewater at all levels, the terminal wastewater deep treatment water production is about 404.5 m3/d. The primary pollutant concentrations are COD 7.52 mg/L, ammonia nitrogen 0.11 mg/L, petroleum 0 mg/L, phosphate 0.02 mg/L, and SS 0 mg/L, which meets the requirements of "process and product water" in "Water Quality for Industrial Water Use in Urban Wastewater Recycling" and can be reused for industrial production.
The drainage from the phosphating wastewater treatment facility, the concentrated water from the terminal sewage deep treatment, and the clean sewage is sent to the factory's main drainage outlet. The total wastewater discharge is about 499 m3/d. The emission concentrations of significant pollutants are COD 145 mg/L and total nickel 0.072 mg/L, which meet the requirements of the third-level standards in Table 1 and Table 4 of the "Integrated Sewage Discharge Standard" and meet the discharge standards. The wastewater is discharged into the sewage treatment plant through the municipal sewage network for further treatment and then discharged to the outside.
The designed treatment capacity of each wastewater treatment unit is shown in Table 3. The water volume to be treated by each unit of the wastewater treatment facility is phosphating wastewater treatment facility 208.2 m3/d, comprehensive wastewater pretreatment facility 339.3 m3/d, terminal wastewater treatment facility 539.3 m3/d, terminal wastewater deep treatment facility 539.3 m3/d. Considering the adjustment coefficient of 1.3, the designed treatment capacity of the four wastewater treatment systems is 270 m3/d, 840 m3/d, 1,800 m3/d, and 800 m3/d, respectively, which can meet the company's production wastewater treatment needs.
| Treatment unit | Equipment/facility | Quantity | Effective volume or flow rate of a single pool | Designed treatment capacity/(m3·d-1) | Forecasted treatment capacity after expansion/(m3·d-1) | Remarks |
| Phosphate wastewater treatment | Waste liquid collection tank | 1 | 2 m3 | 270 | 208.2 | Intermittent operation |
| Ni-containing wastewater regulating tank | 1 | 320 m3 | Intermittent operation | |||
| Lamella Clarifier | 1 | 300 m3 | Single shift operation | |||
| Coagulation tank | 1 | 8 m3 | Three-shift operation | |||
| Comprehensive wastewater pretreatment | Waste liquid collection tank | 2 | 340 m3 | 840 | 339.3 | Intermittent operation |
| Coagulation tank | 1 | 320 m3 | Three-shift operation | |||
| Air flotation sedimentation machine | 1 | 70 m3 | Three-shift operation | |||
| Terminal wastewater treatment | SBR Reactor | 4 | 650 m3 | 1800 | 539.3 | Two-shift operation |
| Clean water pool/flow pool | 1 | 80 m3 | Two-shift operation | |||
| Terminal wastewater advanced treatment | Multi-media filtration | 1 | 50 m3 | 800 | 539.3 | Two-shift operation |
| Ultrafiltration/reverse osmosis dual mode device | 1 | 50 m3 | Two-shift operation | |||
| Sludge treatment | Sludge pool | 2 | 65 m3 | Single shift operation |
Table 3 Designed treatment capacity of each sewage treatment unit of an automobile manufacturing company
The wastewater generated in the coating production process has the characteristics of many types of pollutants, such as high concentration, complex composition, intermittent discharge of sewage and irregular discharge time, poor biodegradability, etc. Only by rationally selecting wastewater treatment methods and designing treatment processes that meet the requirements of enterprises according to different process characteristics by local conditions can the wastewater treatment efficiency be improved, the treatment cost can be reduced, and the treatment cycle can be shortened.
